Made in the Shade

Urban trees can help beat the heat -- and save money for city governments.

Tools

With this summer's heat, many cities are wishing they had more green space -- if for no other reason than to give pedestrians a shady oasis. The "heat island" effect of densely developed spaces causes urban air to be up to 10 degrees hotter than the surrounding countryside, according to the Environmental Protection Agency.

Trees cool the air, reduce pollution, and absorb storm-water runoff, say forestry experts. But the benefits aren't only ecological. Property values are 18 to 25 percent higher for houses surrounded by trees, and consumers spend up to 13 percent more at shops near green landscapes.

Dragged kicking and screaming -- and sweating -- citizens and civic leaders are finally understanding the importance of the "urban tree canopy."

"Every city we've looked at -- about three dozen -- shows a decline of about 30 percent of the urban tree canopy in the past 10 to 15 years," says Deborah Gangloff, executive director of American Forests. In some cities, the loss from disease, development, and neglect has been catastrophic. In Washington, D.C., for example, 64 percent of heavily forested areas disappeared between 1973 and 1997. In the next 50 years, total American land mass reclassified from forest to urban is expected to equal the size of Montana, suggests U.S. Forest Service data.

To reverse the trend, cities like Jacksonville, San Francisco, Albuquerque, Des Moines, and Indianapolis have ambitious urban reforestation plans. Los Angeles wants to plant 1 million trees. Washington, D.C., is partnering with tree-planting groups and nonprofits such as the Casey Trees Endowment Fund, an organization with a $50 million grant to combat the precipitous canopy decline. The fund's urban forester program trains volunteers to conduct on-site censuses that locate, measure, and identify every tree in the city.

The data collected is crunched by a U.S. Forest Service computer model, which produces a precise environmental and economic value for each tree. For example: A 50-foot American linden on a busy city street stores 1,476 kilograms of carbon and removes 123 grams of sulfur dioxide from the atmosphere each year.

Urban trees also reduce flow of pollutants into rivers and storm-water runoff, a problem largely caused by impervious surfaces such as concrete.

A 2005 study of Boulder, Colorado's municipal trees found that the average tree intercepts 1,271 gallons of storm water annually, saving the city $523,311 in storm-water retention costs.

For municipalities already struggling to meet the Environmental Protection Agency's air-quality goals and build adequate wastewater treatment facilities, urban trees offer high return on investment. The Boulder report estimates the city gets $3.67 return on every dollar spent on the urban forest.

"It's worth considering the value of these trees when making policy decisions," explains Dan Smith, a Casey Trees spokesman. "Why would such a relatively small federal program that is providing extremely important research be on the chopping block?" Like the urban trees themselves, the programs must be nurtured. All told, a whopping 634 million trees will be needed to meet American Forests' "National Urban Tree Deficit" canopy coverage recommendations. And that's nothing to shake a stick at.

Ethan Gilsdorf is a Boston writer. This article first appeared in The Christian Science Monitor.